In the first four months of 2013, Channel 4's share of total UK viewing dropped to 6.0%, compared with 6.8% during the same time period last year. Among 16- to 34 year-olds it fell from 8.7% to 8.2%.

These figures include the ratings for Channel 4+1. If the +1 channel's ratings are stripped out then the picture is bleaker, with the main channel averaging, across the day, an audience share of 5.1% – compared with 5.8% last year.

BBC2's all-hours audience share for the year to date is down to 5.3%, from 6.5% for the same period in 2012.

Channel 4's decline is being put down to the fact that hit shows such as Homeland and Big Fat Gypsy Wedding specials aired during the first half of 2012, plus the impact of changes to the BBC1 and BBC2 daytime schedules.

In the year to 9 May, Channel 4's audience share between 3.10pm and 5pm dropped from 11.9%, year on year, to 7.6%, while BBC1's grew from 4.2% to 13.2% and BBC2's fell by around half.

BBC1's all-hours audience share is up from 20.4% to 21.4% and ITV is also up very marginally year on year so far in 2013, from 16.37% to 16.41% (including ITV1+1 – 0.9% year to date). Channel 5 has dipped slightly, from 4.69% to 4.36% (including C5+1 – 0.4%).

In peak time, Channel 4 is facing a similar ratings scenario, averaging 6.2% (including C4+1), down from 7% during the first five months last year. The Channel 4 network, excluding C4+1, is averaging 5.4%, down from 6% in 2012.

The Channel 4 portfolio of channels – including E4 and More4 – is broadly flat year on year, just 1% down at 11.2% audience share. But the broadcaster said there is encouraging news with the launch of 4Seven – a new digital channel providing further opportunities to catch up on Channel 4's most popular and talked-about shows.

Despite winning a Bafta for its coverage of the Paralympics and being lauded for programmes such as The Last Leg, the ratings trajectory for Channel 4 so far is said to be causing some concern within the broadcaster, particularly after the focus on bonuses in coverage of its recent annual report.

However, the return of Homeland and more Gypsy Wedding specials later this year is likely to improve ratings.

A spokesman for Channel 4 said that in terms of 16- to 34-year-olds, including 4Seven and the C4+1 channel, the main network is down just 1% year on year at 8.64%.

He commented: "Channel 4 has continued to launch more new programming in its schedule than any other broadcaster. The range of distinctive content we have broadcast – from Utopia and Complicit, through to the award winning Channel 4 News and the likes of Skint, Gogglebox and the King in the Car Park – has both delivered to 4's remit and helped maintain our channel portfolio share of audience."

It is not yet known what audience share targets Channel 4's executives have been set for 2013.

It was not revealed at the annual report – during which chairman Lord Burns was quizzed about executive bonuses being awarded when the broadcaster reported an audience share of 6.6%, which was short of the target of between 6.8% and 7.1%.

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